In a laser printer, printing is achieved by first scanning a digitized image onto a photoconductor. Typically, the scanning is performed with diodes, e.g. laser diodes or light emitting diodes that pulse a beam of energy onto the photoconductor. The photoconductor typically comprises a movable surface coated with a photoconductive material capable of retaining localized electrical charges. The surface of the photoconductor is divided into small units called pixels. Each pixel is capable of being charged to a given electrical potential, independent of the electrical charge of each surrounding pixel.
In operation, the pixels are first charged to a base electrical charge as they move past a charging unit during each revolution of the photoconductor. Then, as the pixels move past the diodes, the beam of energy, e.g. a laser, is pulsed to remove the electrical charge from the selected pixels. The unaltered and altered pixels thus form an image on the photoconductor. One portion of pixels will attract toner, while the other portion will not based on various factors such as the electrical potential of the toner.
Next, the toner is transferred to a finished product medium, e.g. paper, transparency, fabric. After the toner is transferred to the finished product medium, the toner is affixed thereto. Any residual toner on the equipment is then removed by a cleaning station.
The digitized image is essentially organized into a two dimensional matrix within a raster. The image is digitized into a number of lines. Each line comprises a number of discrete points. Each of the points corresponds to a pixel on the photoconductor. Each point is assigned a binary value relating information pertaining to its color and potentially other attributes, such as density. The matrix of points makes up the resultant digitally stored image. The digital image is stored in computer readable memory as a raster image. Video blocks or scan control circuitry read the raster image data and actuates the laser to selectively expose a given pixel based on the presence or absence of coloration, and the degree of coloration for the pixel. For a four-color laser printer, at least one laser scanner is included in the printer and used to generate a latent electrostatic image on the photoconductor. Generally, one latent electrostatic image is generated for each color plane, e.g. cyan, yellow, magenta, and black, to be printed.
One prior art four-color laser printer is a four-pass that includes a single photoconductor and a single laser/mirror scanner system. In operation, each of the four color planes which make up an output image is consecutively developed on the photoconductor and completely deposited on the intermediate transfer device. A characteristic of the four-pass printer is that the size of output image produced thereby is limited by the length of the intermediate transfer device, since the entire output image is produced in its entirety on the intermediate transfer device before the image is transferred to the finished product medium.
Another prior art four-color laser printer is an in-line that includes four lasers and four in-line photoconductors. Each of the lasers is paired with one of the photoconductors. Also, each of the four colors of toner corresponds exclusively to one of the laser/photoconductor pairs. During operation of a typical in-line printer, each of the four color planes is developed on its own corresponding photoconductor and then deposited on the intermediate transfer device or, as in an alternative configuration, directly on the finished product medium. Generally, all of the color planes of a given image produced by an in-line printer are produced concurrently.
Current video blocks are designed for one type of printer. Thus, a video block used for a single beam in-line printer cannot be applied to a dual beam video laser printer. While a dual beam video block can be used in a single beam application, the silicon real estate is wasted.